Communicating system



May 3, 1938. 2,115,914

J. R. MaCKAY COMMUNICATING SYSTEM Filed June 11, 1934 7 sheets-sheet' 1 INVENTOR 7 ATTORNEY G May 3, 1938. J. R. MaoKAY 2,115,914

COMMUNICATING SYSTEM Filed June ll, 1934 7 Sheets-Sheet 2 l N n v L@ l NvENToR AT-roRNgYs May 3, 1938.

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COMMUNICATING SYSTEM Filed June 11, 1954 '7 Sheets-SheetI 4 ATTORNEYS May 3, 1938. J. R. MacKAY 2,115,914

COMMUNICATING SYSTEM Filed June l1, 1913 7 Sheets-Sheet 5 EZER 527 ATTORNEYS J. R. MaCKAY May 3, 193s.-

COMMUNI CAT ING SYSTEM Filed June l11, 1954 7 sheets-sheet 6 INVENTOR |Il BY @MTW 2f;Aw f AMJ@ ATTORNEY S mwa www

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COMMUNICATING SYSTEM Filed June 11, 1934 '7 Sheets-Sheet 7 BY Mgr .T Suk ATTORNEYS Patented May 3, 1938 UNITED STATESv PATENT OFFICE COMMUNIOATING SYSTEM Application June 11, 1934, Serial No. 730,127

30 Claims.

This invention relates to communicating systems. More particularly it relates to telephone systems and from a still more specific aspect it relates to radio telephone systems.

One of the ob-jects of the invention is to provide a two-way radio telephone system in which 'the user at the calling station operates a call switch and the user at the called station receives a signal, as the ringing of a bell, thereupon lifts his telephone receiver from its hook, and thereby the user at the calling station is given a signal, as by means of a bell, indicating that his call has been put through, and the user at the calling station thereupon removes his telephone receiver from its hook, and two-way telephone conversation may then proceed as in the case of an ordinary communication over two land line telephones which have been properly connected.

A further object of the invention is to provide a radio telephone system in which the major portion of the apparatus employed is not energized at all times but only periodically at such desired intervals as will conserve the energy required to energize or activate such apparatus.

Further objects are to provide new combinations of instrumentalities and new sub-combinations thereof whereby the communication system is comparatively inexpensive to build and operate, comparatively simple in operation from the standpoint of the intelligence required to use it, and thoroughly reliable in its operation. Other objects and advantages will appear as some of the preferred forms of the invention are hereinafter disclosed.

Referring to the drawings which illustrate what I now consider to be preferred forms of the invention:

Figs. la and 1b are wiring diagrams of apparatus at two separated stations between which communication is to be established and maintained; station A (Fig. la.) showing the call switch in its calling position and the energization of relays at that station resulting from such operation of the call switch; station B (Fig. 1b) showing the condition of the circuit and position of parts during normal operation with no signal being received and with the cam operated switch in its normally open position.

Fig. 2a is a wiring diagram of thel apparatus at the master station of a different form of the invention.

Fig. 2b is a wiring diagram of the apparatus at one of a group of stations adapted to be selectively called from the master station of Fig. 2a.

Fig. 3a is a wiring diagram of the apparatus at (Cl. Z50-9) a master station in a somewhat modified form of system; Fig. 3a being in general respects similar to Fig. 2a.

Fig. 3b Ais a wiring diagram of the apparatus at one of a group of stations adapted to be selec- 5y tively called from the master station shown in Fig. 3a.

Fig. Li, is a wiring diagram of a still further modified form of system; the wiring diagram shown in this figure being that of any one of a group of stations in a system.

Referring first to Figs. 1a, 1b in order to facilitate explanation, it will be assumed that station A is the calling station and that station B is the called station, it being understood that either station may be the calling or called station.

Before proceeding with the construction and electrical connections ofthe control system it should be understood that the conductor 20 is connected with the output, such as the plate circuit of the detector stage, of. a suitable vacuum tube wireless receiving apparatus (not shown). This receiver may be of standard and well-known construction. So far as the features of invention disclosed in Fig. 1 are concerned it is immaterial what particular type of radio receiving apparatus be employed and connected to the conductor provided the receiver is adequate for receiving radio telephone signals and converting them to sound frequency speech-representing currents and provided further that th-e receiver shall be capable of producing a suitablechange in current in the conductor 20 in response to the desired received carrier frequency. It is to be understood further that the equipment at each station includes suitable radio transmitting apparatus (not shown) whose iilament and plate supply are rendered operative upon energization of the transmitter control relay 2| so as to emit adesired carrier frequency and also properly to modulate it when telephone conversation takes place in the manner later to be described.

For two-way operation the control apparatus at station A is the same as that at station B.

The construction and connections may be satisfactorily explained by describing the operation of the system assuming that the user at station A desires to call the user at station B and thereafter converse with him as in customary use of two land line telephones connected for that purpOSe.

The user at station A throws his call switch 22 to calling position thereby causing the three normally open contacts of the call switch to become closed.

Operation of the call switch 22 to the calling position establishes the following circuit: from the positive side of a suitable power source, such for example as a '7% volt battery as indicated, through the transmitter control relay 2 I, through the now closed contacts 23 of the call switch 22, back to the negative side of the power source. Energization of the transmitter control relay 2| causes energization of the filament and plate supply of the radio transmitter (not shown) and the latter begins to transmit and continues totransmit a carrier wave of high frequency from station A.

Operation of the call switch 22 to the calling position also closes the following circuit: from the positive side of the 'l1/2 volt battery, through the relay 24, through the contacts 25 of the call switch, back to the negative `side of the 'l1/2 volt battery. Energization of the relay 24 causes the tubes of the radio receiving apparatus at station A to be supplied with energy and also closes the lament circuit of the tube 26.

Operation of the call switch 22 to calling position also places the following signal circuit in condition to be energized if and when the relay 21 becomes energized: from the positive side of the 71A.; volt battery through the signalling device, in the present case a bell 28, through the contacts 2S of the hook switch 3D, through the contacts 3i of the call switch 22, `through the contacts 32 (now open) of the relay 21, back to the negative side of the 'l1/2 volt battery.

By the operation of the call switch 22 to its calling position the radio transmitter at station A has been put into operation to cause to be emitted a high frequency carrier wave (in this case iin-modulated); also the radio receiving fapparatus at the calling station, i. e. station A, has been placed into operative receptive condition; and also the circuit of the bell 28 at station A has been placed in condition to advise the user at station A upon receipt of an answer back in the manner presently to be described.

Turning now to the apparatus at station B I shall first describe the connections and operation of periodically operating or cycling mechanism having for its principal purposes the conservation of apparatus and of energy required.

A motor 33 is provided for continuously rotating a cam 34 which periodically operates the cam switch 35. While this motor may assume a variety of different forms, I prefer at present to employ a motor of the magnetic type such as that described and claimed in the application of Charles F. Wallace, Serial No. 596,072, filed March 1, 1932 for Electric motor apparatus. The circuit of the motor is as follows: from the positive side of the r{1/2 volt battery through the winding of the motor 33, through the normally closed contacts 31 of the relay 21, back to the negative side of the 7% volt battery. 'Ihe motor 33 normally continues to run.

Closure of the contacts 38 of the cam switch 35 connects the relay 24 across the `'I1/2 volt battery. Energization of the relay 24, as stated, causes the tubes of the radio receiver to become energized, also the tube 26.

In short, the motor 33 and instrumentalities just described automatically and periodically cause the tubes of the radio receiver to become energized. By this means the consumption of energy is minimized and the life of the apparatus prolonged.

When the carrier wave of station A (i. e. the calling station) is received by the radio receiver at station B (the called station) and the cam 34 has closed its cam switch 35, the plate current of the tube 25 energizes the relay 40 and closes the following circuit: from the positive side of the '7l/2 volt battery, through the contacts of the relay 4l), through the relay 21, back to the negative side of the 71A; volt battery. Energization of the relay 21 closes its contacts 32 and opens its contacts 31. Opening of the contacts 31 breaks the circuit of the motor 33 so that the motor stops with the high spot of the cam 34 holding the contacts of the cam switch 35 closed.

Closure of the contacts 32 of the relay 21 causes the following circuit to be energized: from the positive side of the l1/2 volt battery, through the bell 28, through the contacts 29 of the hook switch 30, through the contacts 42 of the cam switch 35, through the contacts 32 of the relay 21 and back to the negative side of the '7l/2 volt battery. The bell 28 therefore rings at station B, thereby notifying the attendant at that station that he is wanted on the telephone and the bell continues to ring until he lifts his receiver from its hook, or station A ceases to call. When the user at station B removes his receiver 53 from the hook of the hook switch 35, the contacts 29 are automatically opened and the bell circuit is thereby opened and the bell ceases to ring.

Removal of the receiver from its hook at station B closes the contacts 4I and 43 of the hook switch 33. Closure of the contacts 43 of the hook switch 3B causes the relay 45 to be energized through the following circuit: from the positive side of the 'l1/2 volt battery, through the contacts 43 of the hook switch 30, through the relay 45, back to the negative side of the '7l/2 volt battery.

Closure of the contacts 4I of the hook switch 3l (which are in parallel with the contacts of the relay 45) maintains energization of the relay 21 so that subsequent deenergization of the relay 40 will not cause the contacts 31 of the relay 21 to close and cause rotation of the cam 34 by the motor 33. Though not essential to the proper functioning of the apparatus, it is desirable to prevent rotation of the motor 33 when communication takes place, so as to permit the telephone transmitter or microphone 54 to be mounted on the case which contains the motor, without objectionable background noise due to vibration.

Energization of the relay 45 causes its four sets of contacts to close.

Closure of the contacts 45 of the relay 45 completes the following circuit for the relay 24: from the positive side of the l1/2 volt battery, through the relay 24, through the contacts 46 of the relay 45, back to the negative side of the l1/2 volt battery. This circuit maintains the radio receiver at station B in operative condition.

Closure of the contacts 41 of the relay 45 establishes the following circuit for the relay 50: from the positive `side of the 'I1/2 volt battery, through the contacts 41 of the relay 45, through the relay 59, back to the negative side of the r11/2 volt battery. Energization of the relay 50 disconnects one end of the conductor 20 (the other end of which is connected to say the detector output of the radio receiving apparatus, not shown) from the input or grid circuit of the tube 26, and connects the said end of the conductor 20 to the primary winding of the transformer 52. The secondary winding of the transformer 52, it will be noted, is connected to the telephone receiver or head piece 53. The tube system 26 is biased to cut-off, i. e. suflicient negative biasing potential is applied to the grid of the tube 26 to prevent the flow of plate current when no-external potential is impressed upon the grid.

Closure of the contacts 4S of the relay 45 connects the microphone or transmitter 54 in series with the microphone battery andthe microphone input to the radio transmitter (not shown).

Closure of the contacts t8 of the relay 45 establishes the following circuit through the transmitter control relay 2|: from the positive side of the '7l/2 volt battery through the transmitter control relay 2i, through the contacts 49 of the relayv 45, back to the negative side of the 71/2 volt battery. Energization of this transmitter control relay 2| causes the iilament and plate supplies of the radio transmitter at station B to become operative and to transmit a high frequency carrier wave at a frequency different from that emitted at station A and to which the receiver at station A is tuned.

Except that the frequency of the carrier emitted at station A is different from that emitted at station B and except for the fact that the radio receiving apparatus at station A is tuned to the carrier or station B, and the radio receiving apparatus at station B is tuned to the carrier frequency at station A, the apparatus and connections at stations A and B are identical.

Returning now to the calling station, i. e. station A, the carrier wave transmitted from the called station (station B) is received at station A and causes an increase in the plate current of the tube 25 to energize the relay 4), thereby closing the following circuit through the relay 2: from the positive side of the '7l/2 volt battery, through the contacts of the relay 4U, through the relay 2l, and back to the negative side of the '7l/2 volt battery. Energization of the relay 2l closes the circuit of the bell 28 traced above in connection with station A. The ringing of this bell at station A indicates to the user at that station that his call has been completed and he now removes his telephone receiver or head piece 53 from its hook. This causes the bell circuit to be broken at the contacts 23 of the hook switch 30 and the bell at station A ceases to ring.

Removal of the receiver 53 from its hook at station A also closes the contacts 4l, thereby maintaining energization of the relay 27, thereb-y preventing rotation of the motor 33, as above explained in connection with station B.

Removal of the receiver 53 from its hook at station A also closes the contacts 43 of the hook switch 35 to establish the circuit of the relay 45 as follows: from the positive side of the 7l/2 volt battery through the contacts 43 of the hook switch through the relay d5, and back to the negative side oi the 71/2 volt battery.

This energization of the relay 45 closes the four pairs of contacts of that relay.

Closure of the contacts l5 of the relay 45, which contacts are in parallel with the contacts 25 of the call switch 22 insures that the relay 2A shall be kept energized until conversation has ceased and even though the call switch 22 may have been returned to its off position.

Closure of the contacts 49 of the relay 45, which contacts are in parallel with the contacts 23 of the call switch 22, insures that the transmitter control relay Zi shall be kept energized until conversation has ceased and even though the call switch 22 may have been returned to off position.

Closure of the contacts 4l of the relay 45 connects the relay 56 across the l1/2 Volt battery.

Energization of the relay 55 disconnects one end ofthe conductorA 20 (the other end of which is. connected to say the detector output of the radio receiving apparatus not shown) from the input or grid circuit of the tube. 26 and connects the said end of the conductor 20 to the primary winding of the transformer 52.

Closure of the contacts 48 of the relay 45 connects the microphone 54 to the microphone battery and to the microphone input of the radio transmitter (not shown) rTelephone conversation may now beV carried on between Stations A and B as in the case of persons conversing over ordinary land line telephones whioh have been properly connected, i. e. each person may interrupt the other and in all respects converse in the usual manner.

When conversation has ceased,'the usersv at stations A and B merely hang up their receivers or head pieces 53 on the hooks of the hook switches 30 and the user at station A throws his call switch 22 to the.off position (if the last mentioned switch has not already been moved to the off position) and the parts are all automatically restored to their normal positions.

The tracing of the circuits above and the various sequential actions that automatically take.

place should not lead to 4the impression that the system is complicated in its mode of operation.

Reoapitulating: When the operator at either station desires to call the other station, all that he does is to throw his call switch to calling position. This automatically causes the bell to ring at the called station and when the attendant at the called station removes his telephone receiver from its hoc-k the bell rings at the calling station, the user at the calling station then removes his receiver from its hook and two-way conversation then proceeds. After conversation has ceased each user at his station hangs up his receiver on its hook and the user at the calling station throws his calling switch to the 01T position.

The motor 33 and its associated apparatus and circuits conserve the energy supplied to the system and may be adjusted or set to operate periodically the cam switch 35 at any'intervals desired depending upon the conditions ci service. I have found that in many cases itis advantageous to have the motor 33 operate the cam switch at say 5 to l5 minute intervals, i. e. with intervals of 5 to l5 minutes betweenlsuccessive operations of the cam switch 35. If, as I prefer, the Wallace motor above referred to is employed, the total energy consumption is kept comparatively low since that motor will operate continuously for about a year on ve ordinary dry cells.

The relay 4E) is preferably of a type which closes slowly and opens quickly. This desired operation may be effected by a dash-pot controlled armature or by other suitable means. Such re.- lays of the dash-pot type are commonly used in other circuits such asland line telephone circuits and may readily be acquired in the open market. By providing a relay of this type, the likelihood of false operation due to interfering signals or static is greatly reduced. The system is so designed and operated that the relay 40 will respond to the prolonged carrier received from the other station (A or B) and that carrier will persist and cause closure of the contacts of the relay 45. On the other hand, an interferingsignal or static will be of such comparatively short duration that the relay 40 will not be energized for a suflicient length of time to cause its contacts to close in response to such interfering signal or static. It will be understood that the relay 40 will not respond to a succession of energizations each insufficient to cause its contacts to close because upon each interruption of the energizing current the relay quickly returns to its fully open position. Interrupted continuous wave code signals, for example, would produce interrupted current in the relay 40 and none of the current impulses would be likely to be of suiiicient duration in point of time as to cause the relay 40 to respond sufficiently long to close its contacts. As stated, other suitable forms of retarded relays may be employed.

While not essential, I prefer to provide a pilot light at each station to indicate when the call switch at that station has been operated to its calling position and to indicate the operation of the motor 33 at that station. The pilot light B0 is shown connected at one side to the positive side of the 7 1/2 volt battery and its other side to the contacts 25 and 38 in parallel and thence to the negative side of the '7% volt battery. By virtue of these connections the pilot light 60 will light when the call switch 22 at its station is moved to calling position, and the pilot light will light also whenever the contacts 38 are closed by the cam switch 35 at that station. The pilot light blinks or flashes in response to periodic closure of the cam switch contacts 38, thus providing a visual monitoring of the apparatus. i

The particular circuit illustrated includes a suitable by-pass condenser 6| across the relay 40, a by-pass condenser 62 to complete the high frequency path of the grid circuit of the tube 26 and a by-pass condenser 64 which by-passes the B battery. A rheostat 65 is shown for the purpose of controlling the lament current of the tube 25. A volume control potentiometer 6E is shown shunted across the head piece or telephone receiver 53; it being understood that this may be dispensed with and suitable volume control provided elsewhere in the radio receiving apparatus if desired.

A condenser 61 and resistance 68 shown connected across the contacts 42 provide a means for suppressing sparking or arcing at these contacts which are included in the circuit of the bell 28.

In Figs. la and lb, as stated, I have not shown either the radio receiving or the radio transmitting apparatus employed at each station. It will be understood that radio waves of one carrier frequency emanate from the radio transmitting set of station A, are received by the radio receiving set at station B, and are translated thereby and supplied to the conductor 20 at station B. It will also be understood that radio waves of a different carrier frequency emanate from the radio transmitting set at station B, are received by the radio receiving set at station A and are translated thereby and supplied to the conductor 20 at station A.

In the forms of invention thus far described, an unmodulated carrier wave is employed for calling the desired station. My invention ernbraces other methods of e'ecting the calling; for example, in certain forms of invention hereinafter described, use is made of a modulated carrier for effecting the calling.

In Figs. 2a and 2b, I have diagrammatically illustrated another form of my invention, in which a master station represented by Fig. 2a is enabled to call selectively any one of a number of individual stations which, for convenience, may be termed slave stations, so that any selected one of such slave stations may be called without apprising the operators at any of the other slave stations that the call is being made. In this particular form of the invention any of the slave stations may call the master station, but they cannot inter-communicate with each other.

In this form of the invention, the master station employs one carrier frequency which is modulated in such fashion as to impart to it the desired selective characteristic to which a selected slave station will respond. In the particular arrangement illustrated provision is made for selectively calling any desired one of four slave stations from the master station; it being under,- stood that the system may be used in connection with more or less of such slave stations.

The master station (Fig. 2a) embodies apparatus much of which will be now recognized in View of the description of the foregoing embodiments of the invention; it, however, departs in some respects, as will appear.

Let it be assumed that the user at the master station A desires to call station B. The call switch 400 corresponding to station B or call B, is thrown to calling position, thereby closing contacts 40| to establish the following circuit through the relay 402: from the positive side of a source of energy, in this instance a 71/2 volt battery, through the wires 50|, 403, through the contacts 40| of the call switch 400, through the wire 404, through the relay 402, through the conductors 405, 05,back to the negative side of the 7%? volt battery. Operation of the call switch 400 to calling position also causes closure of the contacts 401 to establish the following circuit: from one side of the microphone input through the conductor 408, through the shaft or common connection 409 of a series of current interrupting devices, through the particular current interrupting device 4|0 (corresponding to call B), through the contacts 401, through the conductor 4| I, through the contacts M2 of the relay 402, through the conductor 4|3, through contacts 4|4 (now closed) of the relay 500, through the conductor 4|5 to the microphone battery, which in turn is connected at 4|6 to the other side of the microphone input.

Closure of the contacts 40| by throwing the call switch 400 to the calling position, also closes the following circuit of a motor 4H: from the positive side of the 'l1/2 volt battery through the conductor 403, through the contacts 40| (now closed) through the motor 4| "i, through the conductor 4|8, through the contacts 4|9 (now closed), back to the negative side of the *.71/2 volt battery.

The motor 4H, when energized, rotates circuit-interrupting devices (in the present case four in number), of which one, 4H), has been referred to. Each of these four circuit-interrupting devices so operates as to produce the particular interrupting characteristic corresponding to the call of the particular selected slave station.

Energizaticn of the relay 402 in the manner described, also closes the contacts 432 to energize the transmitter control relay (not shown) as to cause the radio transmitting apparatus to become operative; the circuit being as follows: from the 'Z1/2 volt battery, through the conductor 433, through the transmitter control relay, through the conductor 434, through the contacts 432 (now closed), through the conductors 405, 406, back to the negative side of the '7l/2 volt battery.

As thus far described, operation of the call switch 40B to calling position has called the radio transmitting apparatus at the master station (A) into operation and the transmitting apparatus is now emitting a carrier frequency modulated in accordance with the particular characteristic of l the current-interrupting device 4| 0.

Energization of the relay 402 at the master station, as above described, causes the radio receiving apparatus at the master station tobeplaced in condition to receive. Closure of the contacts 429 of the relay 4532 causes the following circuit, including the relay 42|, to be closed: from the positive side of the '7 1/2 volt battery, through the conductor 422, through the relay 42|, through the conductor 423, through the conductor 424, through the contacts 420, through the conductors 405, 466, back to the negative side of the 'l1/g volt battery. Energization of the relay 42| closes the iilament circuits of the tube 425 and also oi the receiving apparatus at the master station. Energization of the relay 442 also closes the contacts 426 to place the circuit of the bell 421 in condition to be fully closed to ring the bell if and when the contacts 428 are also closed; the bell circuit being as follows: fromv the positive side of the 7% volt battery, through the conductor 422, through the bell 421, through the contacts 425 (now closed), through the contacts 426 (now closed), through the conductor 435, through the contacts 428 (now open), through the conductor 43|, back to the negative side of the 7%; volt battery.

Turning now to the particular called station B, I shall first describe the circuit of the Wallace motor, which was described in connection with the preceding forms of my invention, and which is vpreferably embodied in the form of invention now being described. 'I'he motor circuit is: from the positive side of the 'l1/2 volt battery through the conductors 436 and`431, through the conductor 438, through the motor 435, and then through the contact 439, through the conductors 44| and 442, back to the negative side of the 'l1/2 volt battery.

The high spot 444 of the motor driven cam 443 periodically closes the contacts 445 to energize the relay 446 in the following circuit: from the positive side of lthe 'l1/g volt battery, through the conductor 436, through the relay 446, through the conductor 441, through the conductor 446, through the contacts 445 (closed when the high spot or" the cam is in operative position), through the conductors 44| and 442, back to the negative side of the r{1/2 volt battery. Thus, by the operation of the motor 435, the relay 446 is periodically energized. When the relay 446 is energized it closes contacts 445 to energize the filament of the tube 455 and likewise the laments of the radio receiving apparatus at station B, so as to place the same in operative or receiving condition. Thehigh spot 444 of the motor driven cam 443 also periodically closes contacts 45| so as to energize the circuit of the bell 452 if and when the contacts 455 are also closed; the bell circuit being as follows: from the positive side of the 'li volt battery, through the conductors 436 and 431, through the bell 452, through the contacts 454 (now closed) of the hook switch 455, through the cam operated contacts 45|, through the contacts 453 (now open), through the conductor 456 back to the negative side of the 71/2 volt battery. As thus far described it has been assumed that no signal is being received at station B.

in connection with the `foregoing description of the master station A, Fig. 2a, it was explained that the operation of the call switch 466 at the master station causes the radio transmitting apparatus at that station to emit the carrier frequency modulated in accordance with the particular slave station it was desired toA call, i. e.

.under the assumption made, station B. When such modulated signal is received at station B it is impressed upon the grid circuit of the tube 455 through the contacts 451, and causes an increase in plate current of the tube 456 (during the intervals in which the receiving apparatus at station B is operative) to energize a selective relay 458 in the following circuit: from the plate of the tube 456, through the conductor 46|, through the contacts 459 (now closed) of the call switch 466, through the conductor 462, through the selective relay 458, through the conductor 463 to the plate source or B battery. The relay 458 is one which is mechanically tuned so as to be responsive to the modulating frequency transmitted from the master station and corresponding to or representing the call of station B. This relay may, for example, be of the tuned vibrating reed type. It will respond, as stated, to the frequency of modulation representing sta.- tion B but will not respond to other modulation frequencies, whereby the desired selection is obtained. When the relay 458 is energized it closes the circuit across the conductors 464 and 465 to establish the following energizing circuit for the relay 466: from the positive side of the '1l/2 volt battery, through the conductors 436, 465, through the now closed contacts of the relay 458, through the conductor 464, through the relay 456, through the conductor 456, back to the negative side of the 7 1/2 volt battery. Energization of the relay 466 causes the contacts 439 to open so that the motor 435 will stopI (or not continue to run) when the high spot 444 has operated the cam switch 443. In other Words, the reception of the signal to which station B is selectively responsive causes the motor 435 to stop with the high spot 444-of the cam 443 in the position in which the contacts 445 and 45| are closed. Energization of the relay 466 also causes the contacts 453 to close whereby the circuit of the bell 452, traced above, is closed to cause the bell to ring.

When the user at station B hears his bell 452 he removes his receiver or head-piece 416 from the hook of the hook switch 455 thereby automatically opening the contacts 454. This opening of the contacts 454 interrupts the circuit of the bell 452 and the bell ceases to ring. Removal of the receiver or head piece 41-6 from the hook switch also causes the -contacts '41| to be automatically closed to energize the relay 412 in the following circuit: from ythe positive side of the 71A, volt battery, through the conductor 436, through the conductor 413, through `the conductor 414, through the hook Yswitch contacts 41| (now closed), through vthe relay 412, through the conductor 442, back to the negative side of the I1/2 volt battery.

Removal of the receiver or head Ypiece 410 from its hook causes closure of the contacts -468 of the hook switch 455 to maintain energization of the relay 466 so that subsequent deenergization of the relay 458 will not cause the relay 466 to become deenergized and thereby cause rotation of the motor, such operation being undesirable at this stage, for reasons previously set forth.

Energization of the relay 412 closes the contacts 415 so as to maintain energization of the iilament control relay 446 of the radio receiving apparatus, the maintained vcircuit being as follows: from the positive side of the 'l1/2 volt battery, through the conductor 436, through the relay 446, through the conductor 441, through the contacts 415 (now closed), through the conductor 442, back to the negative side of the 'Z1/2 volt battery. Energization of the relay 412 also,

causes the contacts 416 to close to connect the microphone transmitter 411 to the microphone input circuit of the radio transmitting apparatus at station B, the circuit being as follows: from the microphone battery, through the conductor 418, contacts 416 (now closed), microphone 411, conductor 419 to the microphone input, whose other side is connected to the other terminal of the microphone battery by the conductor 488.

Energization of the relay 412 also causes the contacts 48| to close the following circuit to the transmitter control relay at station B so as to render that radio transmitting apparatus operative to transmit the carrier back to the calling station, i. e. in this instance the master station: From the positive side of the 'Z1/2 volt battery through the conductor 436, through the conductor 482, through the transmitter control relay, through the conductor 483, through the contacts 48| (now closed), through the conductor 442 back to the negative side `of the r11/2 volt battery. Energization of the relay 412 also causes the contacts 484 to close t energize the relay 485 in the following circuit: from the positive side of the rIl/g volt battery, through the conductors 436 and 413, through the contacts 484, through the conductor 486, through the relay 485, through the conductor 481, back to the negative side of the 71/2 volt battery. Energization of the relay 485 opens the above mentioned contacts 451 and thereby disconnects the output of the radio re ceiving apparatus (not shown in this iigure) from the grid of the tube 450 and connects the output of such radio receiving apparatus through the contacts 488 (now closed) to one side of the primary of a transformer 489 whose other terminal is connected to the plate supply or B battery. The secondary of the transformer 489 is connected directly to the head piece or receiver 410.

When the radio transmitting apparatus at station B is rendered operative as above described, it transmits a carrier (which in this instance is unmodulated) which is received at the calling station, i. e. in the case being explained, the master station (Fig. 2a).

When the carrier so transmitted from the called station B is received at the master station (Fig. 2a.) the carrier causes the output of the radio receiver at station A (not shown) to so energize the grid circuit of the tube 425, through the contacts 490 as to cause the plate current of the tube 425 to be increased and thereby energize the relay 49|. 'I'his relay 49| is of the slow acting type previously described with respect to Figs. la, and 1b. Sustained energization of the relay 49| causes the contacts 492 to close thereby energizing the relay 493 in the following circuit: From the positive side of the 71/2 volt battery, through the conductors 50|, 422, through the contacts 492 (now closed) through the conductor 494, through the relay'493, through the conductors 43|, 406, back to the negative side of the '7l/2 volt battery. Energization of the relay 493 causes the contacts 428 to close, thereby closing the circuit to the bell 421, and causing the latter to ring. When the user at the master station Fig. 2a, hears the bell 421 ring he removes his head piece or telephone receiver 491 from the hook of the hook switch 498 thereby automatically opening the contacts 429 to interrupt the circuit of the bell 421. Removal of the head piece 491 from the hook of the hook switch Y584, back to the negative side of the 71/2 volt battery.

Energization of the relay 500 causes the contacts 4|9 to open thereby interrupting the circuit of the motor 4|1. Energization of the relay 500 causes the contacts 4|4 to open and the contacts 505 to close. Opening of the contacts 4|4 interrupts the code modulating circuit to the microphone input and closure of the contacts 505 connects the microphone transmitter 506 to the microphone input in the following circuit: From the microphone battery through the contacts 505, through the conductor 501, through the microphone 506, through the conductors 508 and 408, to one side of the microphone input, the other side of the microphone input being connected, as above described, through the conductor 4|6 to the other side of the microphone battery.

Energization of the relay 500 causes the contacts 509 to close and thus maintain the relay 42| energized in the following circuit: From the positive side of the 7% volt battery, through the conductors 50|, 422, through the relay 42|, through the conductor 423, through the contacts 509, back to the negative side of the r11/2 volt battery. Energization of this relay 42| as described above, insures that the radio receiving apparatus at the transmitting station will be maintained in operative condition.

Energization of the relay 500 closes the contacts 5|0 to cause the relay 5I| to be energized in the following circuit: From the positive side of the 7l/2 volt battery, through the conductor 50|, through the contacts 5|0, through the conductor 5|2, through the relay 5| I, through the conductor 406, back to the negative side of the '7l/2 volt battery. Energization of the relay 5|| disconnects the output of the radio receiving apparatus (not shown) from the grid circuit of the tube 425 and connects such output circuit to the primary 5|3 of the transformer 5|4, the connection being established through the contacts 5|5 of the now energized relay 5||. The head piece or telephone receiver 491 is connected directly across the secondary winding of the transformer 5|4.

The two stations, that is, the master station and the selected slave station B are now in condition for two-way telephone 'speech transmission and reception.

When the conversation has ceased the users on both stations hang up their head pieces on the hooks of the hook switches and the user at the master station restores his call switch 400 to its normal or open position. These simple operations automatically restore the systems to their normal positions.

The foregoing descriptions set forth the sequence of manual and automatic operations resulting from the user at the master station calling slave station B. Except for the difference in the modulating frequency the operation in calling any one of the other slave stations from the master station is similar to that described above. Thus, if the user at the master station desires to call slave station C he would throw the call switch l5I6 to calling position in which event the current interrupting device 5|'| would become effective to impart the particular modulation to the carrier, to which modulation the mechanically tuned relay 458 at station C would respond. If the user at the master station desired to call station D he would throw the call switch 5|8 to calling position to render the circuit interrupting device 5|9 operative and if he desired to call station E he would throw the call switch 520 to operative position in which event the circuit interrupting device 52| would be called into operation. It will be noted that each of the circuit interrupting devices 4|0, 5|'|, 5| 9, and 52| produces different modulating frequencies and the mechanically tuned relay 458 at each slave station is tuned or adjusted so as to respond to a particular one of the four modulating frequencies.

In the event that station B, i. e. one of the slave stations, desires to call the master station (Fig. 2a), the procedure and operation are as follows: The user at station B first throws his call switch 460 to calling position. This operation of the call switch automatically opens the contacts 459 thereby disconnecting the mechanically tuned relay 458 from the plate of the tube 450. Operation of the call switch 460 to calling position also causes the contacts 522 to close thereby placing the non-selective relay 523 in the plate circuit of the tube 450. TheV purpose of this as will later more fully appear, is to enable the calling slave station to respond to an unmodulated carrier to be transmitted back from the master station when the user at that station has responded to the call from the slave station by removing his head piece from its hook.

As explained in connection with Figs. 1a and 1b, the remainder of the operations at station B responsive to throwing the call switch 460 to calling position is to cause a carrier to be transmitted from station B and to place the receiving apparatus at station B in receptive condition for the carrier that will come back from the called station, in this instance, the master station (Fig. 2a)

Turning now to the master station (Fig. 2a) it will be helpful first to describe the circuits of the motor 524 and the instrumentalities controlled thereby.

As in the case of above described forms of invention, the motor 524 is preferably of the Wallace type and it operates a cam 525 having a high spot 526 for operating two sets of contacts. The circuit of the motor 524 is from the positive side of the 'I1/2 volt battery, through the conductors 50|, 422, thence through the winding of the motor 524, through the automatically operated switch 52'2l of the motor (this switch being a part of the standard Wallace motor) and then through the contacts 528, to the conductor 406 and back to the negative side of the 'l1/2 volt battery. The cam operated switch comprises contacts 530 and 53|. When the contacts 530 are closed due to the arrival of the high spot 526 of the cam 525 at a predetermined position once during each revolution of the cam., the following circuit is established through the relay 42|: from the positive side of the 71/2 volt battery, through the conductors 50|, 422, through the relay 42|, through the conductor 423, through the contacts 530, and the conductor 406 back to the negative side of the 'l1/2 volt battery. As previously described, energization of the relay 42| causes the filament of the tube 425 and the filaments of the tubes of the radio receiving apparatus (not shown) at the master station to become energized and the receiving apparatus to become operative for reception. Closure of the contacts 53| by the cam operated switch places the circuit of the bell 421 in condition to be energized when the contacts 428 are also closed by energization of the relay 493; the bell circuit being as follows: from the positive side of they 71/2 volt battery, through the conductors 50|, 422, through the bell 421, through the contacts 429 (now closed) of the hook switch 498, through 'the contacts 53 l, through the wire 430, through the contacts 426 and through the conductors 43|, 406 back to the negative side of the 'l1/z Volt battery.

When the calling carrier transmitted from the slave station B is received at the master station (Fig. 2a) during the interval of time in which the high spot 526 of the cam 525 has operated the cam operated switch as above described, the relay 49| closes its contacts 492 to energize the relay 493. The contacts 428 and 53| now being closed, the bell 421 is energized and rings. The user at the master station now removes his head piece 49`| from the hook of the hook switch 498 thereby closing the circuit of the relay 493 at the contacts 495 and interrupting the bell circuit at the contacts 429. The removal of the head piece 491 fromits hook also automatically causes the co-ntacts 499 to close to energize the relay 560 as has been previously fully described. The operations resulting from energization of the relay 500 are the same as described abo-ve, but the following additional operation should be noted. The call switches 400, 5|6, 5|8, and 520 are at this time all in open position and theV relay 402 is deencrgized. Therefore the transmitter control relay at the master station Will not have been energized due to energization of therelay 432. When, however, the relay 500 is energized it causes the contacts 532 to close and thereby establish the following circuit including the transmitter control relay: from the positive side of the 'l1/2 volt battery, through the conductor 433, through the transmitter control relay, through the conductor 434. through the contacts 532, through the conductor 504, back to the negative side of the 7l/2 volt battery. The transmitting apparatus at the master station now sends out a carrier (in this case not modulated), to which the relay 523 at station B (Fig. 2b) responds and produces energization of the relay 466 and closure of the circuit of the bell 452 at station B. The use-r at station B, upon hearing his bell 452, removes his headpiece 420 from the hook of the hook switch 455 and thereupon two-way telephone conversation may take place as will now be clear in View of the foregoing descriptions. After the conversation has ceased,

the parts are restoredto their normal positions by restoring the head pieces 470 and 49'? to their respective receiver hooks and by restoring the call switch 466 at station B toits normal, that is, noncalling position. v

In Figs. 3a and 3b I have shown wiring diagrams of a master station and one of the slave stations in which a modified form of my invention is embodied. As in the case of the form of invention shown in Figs. 2a and 2b, the system is such that the user at the master station can selectively call any one of a number of slave stations and each of the slave stations may call the master station.

Since, however, the particular circuits shown in Figs. 3a and 3b diiferin various respects from those previously described, I shall trace in some detail the various circuits of the modified system,

proceeding rst with the master station as shown in Fig. 3a.

- The apparatus at the master station comprises a motor of the Wallace type having a winding 600 and an automatically operated circuit interrupter 60|. The circuit of the motor is as follows: from the positive side of the '7l/2 volt battery, through the conductors 602, 664, the winding 660 of the motor, conductor 605, contacts 606 (now closed), conductor 601, contacts 60|, conductor 608, contacts 60S, conductors 6I() and 604 back to the negative side of the '1l/2 volt battery. The motor 600 continuously rotates a cam disk 6H having a high spot 6I2 for closing once during each revolution of the cam disks the contacts 6|3. When contacts 6 I 3 close the relay 6 I4 is energized in the following circuit: from the positive side of the 'Y1/2 volt battery, through the conductors 662, 603, through the relay 6i4, through the conductors 6|5, through the contacts I6|3, through the conductors 6|6, 6|0 and 604 back to the negative side of the 'I1/2 volt battery. Energization of the relay 6|4 causes the contacts 6 I1 to close, thereby closing the lament circuits of the tube BIB and the filament circuits of the tubes of the radio receiving apparatus, not shown.

From the description of Fig. 3a as thus far set forth, it will be apparent that the motor 600 operates the cam 6I| so as periodically to close the contacts 613 and during each such closure of the contacts 6|3, the radio receiving apparatus at the master station is placed in operative receiving condition.

The circuits for establishing a call from station A to select one of the desired slave stations, for example station B, will now be described.

The user at the master station throws the call y switch 6|9 (corresponding to station B) to calling position thereby closing the contacts 620 and the contacts 62|. Closure of the contacts 620 establishes a circuit through the relay 622 as follows: from the positive side of the 'Z1/2 volt battery, through the conductor 602, through the contacts 620, through the conductor 623, through the relay 622, through the conductors 6I0 and 604 and back to the negative side of the '1% volt battery. Closure of the contacts 620 also energizes the motor 624 which rotates the circuit interrupting device 625, the circuit of the motor being as follows: from the positive side of the r11/2 volt battery, through the conductor 602, through the contacts 62 0, through the motor 624, through the conductor 626, through the conductor 621, through the contacts 626 (now closed) of the hook switch 629, through the contacts 630 of the relay 622, through the conductors 610, 604, back to the negative side of the '7% volt battery. Closure of the contacts 630 by energization of the relay 622 also establishes the circuit through the primary of a buzzer modulating device 63|, which circuit is as follows: from the positive side of the 7l/2 volt battery, through the conductor 602, through the primary winding of the buzzer 63|, through the conductor 621, through the contacts 628 (now closed) of the hook switch 629, through the contacts 630 (now closed) of the relay 622, through the conductors 6|0, 604, back to the negative side of the r11/2 volt battery. The secondary circuit of thebuzzer modulating device 63| is as follows: from the positive side of the microphone battery, through the conductors 632, 633, through the secondary of the buzzer 63|, through the conductor 634, through the contacts 635 (now closed) of the relay 622, through the conductor 636, through the contacts 631 (now closed) of the hook switch 629, through the conductor 638, through the conductor 639, through the contacts 62|, through the current interrupting device 625, through the conductor 640 to one side of the microphone input, the other side of which is connected through conductor 118 to the negative of the microphone battery. Energization of the relay 622 also causes the contacts 64| of that relay to close establishing the following circuit through the relay 642: from the positive side of the l71/2 volt battery, through the conductor 662, through the relay 642, through the conductor 643, through the contacts 64| (now closed) of the relay 622, through the conductors 6|0 and 604 back to the negative side of the '1l/2 volt battery. Energization of the relay 642 causes its contacts 644 to close thereby energizing the transmitter control relay in the following circuit: from the positive side of the '1l/2 volt battery, through the conductors 602, through the contacts 644, through the conductor 645, through the transmitter control relay, through the conductor 646 and then back to the negative side of the r11/2 volt battery. As described in connection with other forms of the invention, the transmitter control relay, when energized, causes theradio transmitting apparatus to become operative and to transmit a carrier wave.

By the operations thus far described and in response to operation of the call switch 6| 9 to calling position for station B, the master station is now transmitting the carrier frequency modulated by the buzzer modulating device 63| and which modulation frequency is periodically interrupted or chopped by the circuit interrupting device 625.

Energization of the relay 642 causes its contacts 641 to close and thereby energize the relay 6|4 through the following circuit: from the positive side of the 'l1/2 volt battery, through the conductors 602, 603, through the relay 6M, through the conductor 6|5, through the conductor 648, through the contacts 641, through the conductor 604, back to the negative side of the r{1/2 volt battery. As explained, energization of the relay 6| 4, places the receiving apparatus at the master station in condition to receive.

Turning now to the particular slave station being called, i. e. station B shown in Fig. 3b, it will iirst be desirable to describe certain of the circuits at the last mentioned station. The apparatus at station B comprises a Wallace motor 650, 65|, whose circuit is the same as that described in connection with the master station (Fig. 3a). This motor at station B operates a cam 652 which in turn operates contacts 653, all as described above in connection with the master station. 'I'he contacts 653 when closed energize the relay 654 through a circuit similar to that described in connection with the relay 6|4 of the master station (Fig. 3a). The relay at station B when energized, energizes the iilament circuit for the tube 655 and also the lament circuits of the radio receiving apparatus at station B, in similar manner to that set forth in connection with the master station with respect to the relay 6|4. During the rst oc# curring interval of time when the contacts 653 are closed and the radio receiving apparatus at station B has been activated, the interrupted buzzer modulated carrier transmitted from the master station is received by the receiving apparatus at station B and causes the plate current of the tube 655 to energize the selective relay 656 in the following circuit: from the plate of the tube 655, through the conducto-rs 651, through the contacts 658 (now closed) of the call switch 659, through the conductor 660, through the winding of the selective relay 656, through the conductor 66|, through the conductor 662, to the positive side of the B battery, or plate supply. 'Ihe selective relay 656 is a mechanically tuned relay which may be of the type described above in connection with Fig. 2b with respect to the relay there indicated as 458. The relay 656 is mechanically tuned so to speak to respond to the interrupted modulated carrier transmitted from the master station and corresponding to the call of station B.

Energization of the relay 656 causes the relay 663 to be energized in the following circuit: from the positive side of the 71/2 volt battery, through the conductor 664, through the contacts (now closed) of the selective relay 65'6, through the conductor 665, through the relay 663, through the conductor 666, back to the negative side of the 7% volt battery.

Energization of the relay 663 closes the following circuit through the bell 661: from the positive side of the '1 1/2 volt battery, through the conductor 664, through the contacts. 668 (now closed) of the relay 663, through the bell 661, through the conductor 669, through the hook switch contacts 618 (now closed), through the conductors 61|, 612, back to the negative side of the '1l/2 volt battery.

Energization of the relay 663 causes the relay contacts 613 to close to energize the relay 614, through the following circuit: from the positive side of the "I1/2 volt battery, through the conductor 664, through the contacts 613, through the conductor 615, through the relay 614, through the conductor 612, back to the negative side of the '7l/2 volt battery.

Energization of the relay 614 causes the relay contacts 616 to open thereby interrupting the circuit of the winding 658 of the Wallace motor and energization of the relay '614 causes the contacts 611 to close` thereby short-circuiting the Winding 658 of the Wallace motor by the following path: from one side of the winding 658, through the conductors 618, 619, contacts 611 (now closed) of the relay 614, conductor 688 to the other end of the winding 650 of the Wallace motor. Opening of the contacts 616 in the motor circuit interrupts the motor circuit as described,

and the short-circuiting of the winding 658 of the motor by closure of the contacts 811 produces a braking torque which rapidly brings the motor to rest with the high spot of the cam 652 in the position in which the contacts 653 are closed and maintained closed. This keeps the radio receiving apparatus at station B in receptive condition.

The bell 661 at the called station B keeps on ringing until the attendant at station B removes his head piece or telephone receiver 68| from the hook of the hook switch 682. By removal of the head piece 68| from the hook of the hook switch the contacts 818 are automatically opened thereby opening the bell circuit and causing the bell to cease to ring.

When the head piece is removed from the hook of the hook switch 682, the contacts 683 are automatically closed to establish the following circuit through the relay 684: from the positive side of the '1 1/2 volt battery, through the relay 684, through the conductor 685, through the contacts 683 (now closed), and through the conductors 61|, 612 back to the negative side of the 7l/2 volt battery. Energization of the relay 684 causes the contacts 686 to close thereby energizing the transmitter control relay in the following circuit: from the positive side of the 7 1/2 volt battery, through the contacts 686 (now closed) through the conductor 681, through the transmitter control relay, through the conductor 688, back to the negative side of the '7l/2 volt battery. Removal of the head piece 68! from the hook of the hook switch '682 causes the contacts 888 to close thereby energizing the primary of the buzzer modulating device 668 in the following circuit: from the positive side of the 71/ volt battery, through the primary winding of the buzzer 688, through the conductors 88|, through the hook switch contacts 688 (now closed), through the conductor 682, through the contacts 693 (now closed) of the relay 614, through the conductor 694, through the contacts 685 (now closed) of the call switch 659, through the conductors 61|, 612, back to the negative side of the 71/2 volt battery. Since the relay 614 is now energized and the call switch at station B is in oif position the following circuit exists, including the secondary of the buzzer modulating device 688: from the positive side of the microphone battery, through the conductors 686, 681, through the secondary of the buzzer modulating device 668, through the conductor 698, through the contacts 699 (now closed) of the call switch 656, through the conductor 188, through the contacts 18| (now closed) of the relay 616, through the conductors 102, 103 to one side of the microphone input, whose other side is connected through the conductor 184 to the negative side of the microphone battery.

Station B is now transmitting a carrier fre quency modulated by the operation of the buzzer modulator 698 and the radio receiving apparatus at the master station has been tuned to respond to such modulated carrier frequency transmitted from station B. Return now to the master station (Fig. 3d), the modulated carrier received from station B causes the current in the plate circuit of the tube 6|8 to energize the relay 185 at the master station. Energization of the relay 185 causes its contacts 186 to close thereby energizing the relay 181 in the following circuit: from the positive side of the 'l1/2 volt battery, through the conductors 682, 683, through the contacts 186, thrcughthe relay 181, through the conductor 188, back to the negative side of the '1l/2 volt battery. The relay 181 is a slow acting relay, that is, one which requires a sustained relatively prolonged current impulse to cause it to operate its contacts. Its contact operating stroke is comparatively slow while the return or restoration stroke, upon deenergization of the relay, is quite rapid. Responsive energization of the relay 181 causes the contacts 186 to close thereby establishing the following circuit 'through the bell 1|8 at the master station: from the positive side of the '1l/g volt battery, through the conductors 682, 603, through the contacts 188 (now closed) through the conductor 1| through the bell 1|8, through the conductors 1| 2, 688, through the hook switch contacts 688 (now closed), through the conductors 6i0, 684, back to the negative side of the '1l/2 volt battery. The bell 1|8 thus is caused to ring at the master station in response to the modulated carrier transmitted back from station B and the user at the master station (Fig. 3a) removes his head piece 'H3 from the hook of the hook switch 628, thereby interrupting the bell circuit at the contacts 686 which automatically open when the receiver is taken from its hook.

Sustained energization of the relay 101 causes its contacts 114 to close thereby establishing the following circuit through the relay 115: from the positive side of the 'l1/2 volt battery, through the conductors 502, 603, through the contacts 1| 4 (now closed) through the conductor 1|S, through the relay 1|5, through the conductor 1|1, 604, back to the negative side of the 7% volt battery. Removal of the head piece 1I3 from the hook of the hook switch 629 at the master station causes the contacts 528 automatically to open thereby interrupting the circuit of the motor 624 and also the primary circuit of the buzzer modulating device 03|. When the motor 624 is deenergized, rotation of the current interrupting device 625 ceases and the circuit of the latter is interrupted and the modulation removed frorn the carrier transmitted from the master station.

When the modulation is removed from the carrier transmitted from the master station, the following operations take place at station B (Fig. 3b): the selective relay 656 at station B becomes deenergized thereby causing the relay S63 to become deenergized. Deenergization of the relay E63 causes deenergization of the relay 614 by interrupting the circuit of the latter at the contacts 613 of the relay 063. Deenergization of the relay E83 causes its contacts 620 to close thereby energizing the relay 52| in the following circuit: from the positive side of the 71/2 volt battery, through the conductor 664, through the relay S2 I, through the conductor 122, through the contacts B20 (now closed) of the relay 633, through the conductor 123, through the conductor 124, through the contacts (now closed) of the hook switch 632, through the conductors 61|, 612 and back to the negative side of the r11/2 volt battery. Energization of the relay 52| causes its contacts 125 to open and its contacts 121 to close. Opening of the contacts 126 interrupts the circuit of the primary winding of the transformer 128 and connects the primary winding of the transformer 129 to the output of the radio receiving apparatus at station B. The head piece or telephone receiver 68| is connected directly across the secondary winding of the transformer 12 0. Removal of the head piece 68| from the hook of the hook switch 682 also automatically opens the contacts 130 of the hook switch, thereby opening the primary circuit of the buzzer modulating device 690. Deenergization of the relay 614 as described above, causes the contacts 10| of the relay B14 to open thereby opening the secondary circuit of the buzzer modulating device 690. Deenergization of the relay 514 and removal of the head piece 08| from the hook of the hook switch 682 causes the following circuit to be established through the microphone transmitter 132: from the positive side of the microphone battery, through the conductors B95, 133, contacts 13| (now closed) of the hook switch 682, conductor 134, transmitter 132, conductor 135, contacts 13G (now closed because relay 614 is deenergized), conductors 102, 103 to one side of the microphone input whose other side is connected by the conductor 104, to the negative side of the microphone battery.

Station B is now in condition for telephone speech communication but the operations by which the master stationis placed in such condition have not yet been described.

When the modulation is removed from the signal-transmitted from station B back to the master station (Fig. 3a) the relay 105 at the master station becomes deenergized thereby deenergizing relay 101. Deenergization of the relay 101 causes the contacts 1 I4 to open thereby opening the circuit of the relay 115 and deenergizing the latter. Deenergization of the relay 101 causes its contacts 131 to close thereby energizing the relay 138 in the following circuit: from the positive side of the 'l1/2 volt battery, through the conductors B02, 603, through the relay 130, through the conductor 139, through the contacts 13.1 (now closed) of the relay 101, through the conductor '|40` through the conductor 14|, through the contactsy 142 (now closed) of the hook switch 629, through the conductors 6|0, 604 back to the negative side of the 'l1/g volt battery. Energization of the relay 138 as described in connection with Fig. 3b, disconnects the radio receiver output from the primary winding of the input transformer of the tube 6|3 and connects the primary of the transformer 143 to the output of the radio receiving apparatus. The head piece 1I3 is directly connected across the secondary winding of the transformer 143.

In view of the fact that the head piece 1|3 is now off the receiver hook and the further fact that the relay 1|5 is deenergized, the following circuit exists through the microphone transmitter 144: from the positive side of the microphone battery, through the conductor 632, through the contacts 145 (no-w closed) of the hook switch 629, through the conductor 146, through the transmitter 144, through the conductor 141, through the contacts 148 (now closed) of the relay 1|5, through the contacts 149 (now closed) of the relay 1|5, through the conductor 150, through the contacts 15| (now closed) of the hook switch 629, through the conductors 152, 640 to one side of the microphone input whose other side is connected to the negative terminal of the microphone battery. It will be noted that this circuit of the microphone transmitter does not include the circuit interrupting device B25 so that even if the latter has been stopped on a dead spot the microphone circuit will nevertheless be complete.

Station B and the master station are now both in condition for two Way telephone speech communication. When conversation is ended the parts are restored to their normal position merely by placing the head pieces at the respective stations back on to their hooks of the hook switches and by throwing the call switch 0|9 at the master station to its off position.

The operations whereby the user at the master station selects any other desired one of the stations C, D and E need not be further described. 1.

As in the case of Figs. 2a and 2b, so also in the form of invention shown in Figs. 3a and 3b, each of the slave stations responds to the particular character of modulation transmitted from the master station when the call switch corresponding to that station has been thrown to calling position.

I shall now proceed to describe the operations when one of the slave stations, say station B, shown in Fig. 3b, desires to call the master station.

The attendant at station B (Fig. 3b) throws his call switch 659 to calling position. Operation of the call switch 659 to called position causes the contacts to close thereby energizing the relay 684 through the following circuit: from the positive side of the '1l/2 volt battery, through the conductor 619, through the relay 684, through the conductors 685, 156, through the contacts 155 (now closed) of the call switch 659, through the 75 conductors 61|, 612, back to the negative side of the 'l1/2 volt battery. Energization of the relay 684 causes its contacts 686 to close thereby energizing the transmitter control relay and thereby placing the radio transmitting apparatus at station B in operation to transmit its carrier frequency. Energization of the relay 664 causes its contacts 151'to close thereby energizing the relay 654 through the following circuit: from Ythe positive side of the 7%; volt battery, through the conductor 664|, through the relay 654, through the conductor 158, through the conductor 159, through the contacts 151 (now closed), through the conductor 612, back to the negative side of the 7 1X2 volt battery. Energization of the relay 654, as above described, places the radio receiving apparatus and the tube 655 at station B in receptive condition.

Operation of 'the call switch 659 to calling position causes the contacts 160 to close and thereby energize the primary winding of the buzzer modulating device 690 through the following circuit: from the'positive side of the '1% volt battery, through the conductor 619, through the primary winding of the buzzer 690, through the conductor 69|, through the contacts 130 (now closed) .of the hook switch 682, through the contacts 160 (now closed) of the call switch 659, through the conductors 61|, 612, back to the negative side of theiYl/g volt battery.

Operation ofthe call switch 659 to calling position closes the contacts 16| to establish the following circuit through the secondary of the buzzer modulating device 690: from the positive side of the Amicrophone battery, through the. conductors 696, 691, through the secondary of the buzzer modulating device 690, through the conductor 698, through the contacts 16| (now closed) of the call switch 659, through the conductor v162, through the contacts 163 (now closed) of the hook switch 682, throughthe conductor 103, to one side of the microphone input whose other side is connected by means of the conductor 104, to the negative side of the microphone battery.

Operation of the call switch 659 to calling posi tion causes the contacts 653 thereof to open and the contacts 164 thereof to close, thereby disconnecting the plate of the tube 655 from the coil of the selective relay 656 and connecting the relay 165 to the plate of the tube 655.

Operation of the call switch 659 at station B (Fig. 3b) has thus produced the following results:

the radio transmitting apparatus at station B is transmitting the carrier frequency modulated by the buzzer modulating device 690, the radio receiving apparatus at station B has been put into receptive condition, and the selective relay 656 has been taken out of circuit so to speak and the relay 165 connected to the plate of the tube 655.

Turning now to the master station (Fig. 3a), the modulated carrier transmitted from station B causes the relay to be energized and to close its contacts 136 thereby causing the relay 101 to be energized. It will be understood that energization of the relay 105 does not take place until the radio receiving apparatus at the master station (Fig. 3a) has been placed into receptive condition by the arrival of the high spot 6 I 2 of the cam 6|| at the position where it closes the cam operated switch 6|3.

Energization of the relay 101 at the master s'tationxcauses the contacts 109 to close thereby closing the circuit through the bell 1|0 and causing the latter to ring.

Energization of the relay 101 causes its contacts 1|4 to close thereby energizing the relay 1|5 in the following circuit: from the positive side of the '7l/2 Volt battery, through the conductors 602, 603, through the contacts 1|4 (now closed) of the relay 101, through the conductor 1 I 6, through the relay 1 I 5, through the lconductors 1|1, 604, to the negative side of the 'l1/2 Volt battery.

The user at the master station now takes his head piece 1 |3 from its hook thereby opening the circuit of the bell at the contacts 606 of the hook switch 629. Removal of the hook switch from its hook at the master station causes energization of the relay 6424in the following circuit: from the positive side of the 'l1/2 Volt battery, through the conductor 602, through the relay 642, through the conductor 643, through the contacts 166 (now closed) of vthe hook switch 629, through the conductors 6|0, 604, to the negative side of the '7l/2 volt battery.

Removal of the receiver from its hook switch at the master station also energizes the primary of the buzzer modulating device 63| in the following circuit: from the positive side of the 71%2 volt battery, through the conductor 602, through the primary of the buzzer modulating device 63|, through the conductor 621, through the contacts 161 (now closed) of the hook switch 629, through the conductor 168, through the contacts 169 (now closed) of the relay 1|5, through the conductors 110, through the contacts 11| (now closed) of the relay 622, through the conductors 6|0, 604 to the negative side of the 'I1/2 volt battery.

The secondary circuit of the buzzer modulating device 63| is complete at this time and is as follows: from the positive side of the microphone battery, through the conductors 632, 633, through the secondary of the buzzer modulating device 63|, through the conductors 634, through the contacts '|12 (now closed) of the relay 622, through the conductors 113, through the contacts 114 (now closed) of the relay 1|5, through the contacts (now closed) ofthe same relay, through the conductor 116, through the contacts 111 (now closed) of the hook switch 629, through the conductors 152, 640 to one side of the microphone input whose other side is connected through the conductor '|18 to the negative side of the microphone battery.

Energization of the relay 642 places the radio transmitting apparatus in operation at the master station. v

Energization of the relay 1|5 causes its contacts 606 to open the circuit of the Wallace motor and energization of the relay 1|5 causes its contacts 119 to close and thereby to short-circuit the winding 600 of the Wallace motor to bring the motor rapidly to rest with its high spot in the position in which the cam operated switch 6| 3 is closed.

The master station is now sending a buzzer modulated carrier to station B.

Returning now to station B (Fig. 3b), the modulated carrier from the master station energizes the relay at station B causing it to close its contacts 160 to energize the relay 663 in the following circuit: from the positive side of the '7 1/2 volt battery, `through the conductors 664, through the contacts (now closed) of the relay 165, through the relay 663, through the conductor 666, back to the negative side of the 7%; volt battery.

Energization of Vthe relay 663 causes its contacts 668 to close to ring the bell661 at station B. Y

Energization of the relay 663-causes its contacts 613 to close to energize the relay 614?.

The user at station Bnow takesV his head piece 68| off its hook, which opens the bell circuit at the hook switch contacts 610, opens the primary circuit of the buzzer modulating device 690 at the hook switch contacts 139, and opens the buzzer modulating secondary at the hook switch contacts 163.

Returning now to the master station (Fig. 3a.), removal of the modulation from the carrier transmitted from station B becauses the relay at stationA to become deenergized and open contacts-106, thereby deenergizing the relayY 101'.

Deenergization of the relay 101 at the master station causes its contacts 1|4 to open and thus deenergize the relay 1|5.

Deenergization of the relay 101 at the master station causes its contacts-131 to close thereby energizing the relay 138.

Energization of the relay 138 disconnects the primary of the transformer 185 from the output of the radio receiving apparatus at the master station and connects the primary of the transformer 143 to the output of the radio receiving apparatus. Itwill be noted that the head piece 1|3 is connected directly across the secondary ofthe transformer' 143.

Deenerg-ization of the relay 1|5 at the master station opens the contacts 166 and thereby opens the primary of the buzzer modulating device 63| at the master station.

Deenergization of the relay 1|5 opens the contacts-114 and thereby opens the secondary circuit of the buzzer modulated device 63| at the master station.

Deenergization of the relay 1 I5 causes its contacts 148r to close, putting the microphone transmitter 144 in circuit as follows: from the positive side of the microphone battery, through the conductor 632, through the contacts 145 (now closed) of the hook switch 629, through the conductor 146; through the microphone transmitter 144, through the conductor 141, through the contacts 148 (now closed) of the relay 1|5, through the contacts 149 (now closed) of the same relay, through the conductor 150, through the hook switch contacts 15| (now closed), through the conductors 152, 640, to one side of the microphone input whose other side is connected through the conductor 118 to the negative side of the microphone battery.

Discontinuance of modulation from the carrier of station A produces the following results at slave station B` (Fig. 3b) to which we now return.

The relay becomes deenergized thereby deenergizing the relay 663. thereby opening the contacts 513 and deenergizing the relay 614.

Deenergization of the relay 614 atstation B places the microphone transmitter 132at station B in circuit as follows: from the positive side ofthe microphone battery, through the conductors 696, 133, through the contacts 13| (now closed) of the hook switch 682, through the conductor 134, through the microphone transmitter 132, through the conductor 135, through the contacts 136 (now closed) of the relay 614, through the conductors 102, 103, to one side of the microphone input whose other side is connected by the conductor 104 to the otherI side of the microphone battery.

Two way telephone conversation may now proceed between the master. station and the slave station B and when such conversation has ceased the parts are restored to their normal'positions by the return of the head piece 68| at both stations totheir hooks and by throwingthe` call switch 659t0- the off position at station B.

In Fig. 4, I have diagrammatically shown. another different form of my invention; The system shown in Fig. 4 represents one of'a plurality of stations, in the present case a. total offive stations, although the system may be applied toa greater or less number. of stations. Inv accordance with this system anyof'the stations can selectively call any desired one of the other" four stations. Each station, through the operationof wave or frequency changing devices which will later be described in more detail, is capable of selectively transmitting either of two different carrier frequencies .which may, for convenience, be referred to as FI and F2, and likewise each station is-capable of receiving at different stagesof operation one or the other of the two frequencies FI and F2. The selection of these frequenciesl is automatically eiectedas will hereinafter appear. The radio receiving apparatus at all five stations is normally tuned to one of the two frequencies, say the frequency FI. When any of the stations calls another station the radio receiving apparatus at the calling station is automatically shifted to the frequency F2 and when any of the stations is answering a call-its radio receiving apparatus is set for reception of the-fre- A connections shown in-Fig. 4 is similar to that employed in connection withthe forms of invention which have been above described, it will'be helpkful to trace the circuits in Fig.- 4 in some detail.

The Wallace motor 802 operates the cam 808 havingfa high spot 804for operatingthe switch 805' and having a switch 806 forming a part of the motor will all be recognized inA view of the preceding descriptions. y

The circuit of this motor is as follows: from the positive side of the'Il/z voltbattery, through the conductors 800', 80|, through the winding 802 of the Wallace motor, through the conductor 801; through the contacts 808, through the conductor 809', through themotor. contacts 806, through the conductorv 8|0, through the contacts 8| through the conductors 8|2, 8|3, 8|4, to the negative side of the. 7.1/2 volt battery. Due to energization of the circuit just traced, the Wallace motor normally continues to rotate and periodically. close the contacts 805, which, when closed, causethe relay 8|1 to be energized-in the followingv circuit: fro-m the positive side of the 'l1/2 Volt battery, through the conductors 800, 8|5, through the. relayy 8|1, through the: conductors 8|6, through thecontacts 805, through the-conductors 8|3, 8|4, back to thenegativeside ofthe '7l/2 volt battery. The relay 8|1, when energized, causes the filament ofv the tube8l8and`the1fila ments of the radio receiving apparatus (not shown) to be energized.'

By the foregoing operations', the tube, 8.| 8: and

the radio. receiving apparatus. are; periodically 75:'

placed in receptive condition so as to respond to the frequency Fl In order to place a call the user throws to calling position the particular one of the call switches 8|9, 828, 82|, 822 corresponding to the one of the other four stations which he desires to call. Let it be assumed in the present case that station A desires to call station B, in which event the call switch 8|9, corresponding to station B, would be thrown from the off to the calling position. Operation of the call switch 8 I 9 to calling position closes the contacts 823 to establish the following circuit through the relay 824: from the positive side of the '1l/2 volt battery, through the conductor 888, through the contacts 823 (now closed), through the conductor 825, through the relay 824, through the conductors 8|3, 8|4, back to the negative side of the '1l/2 volt battery. Closure of the contacts 823, by operation of the call switch 8|9, also closes the following circuit through the motor 826: from the positive side of the '7l/2 volt battery, through the conductor 888, through the contacts 823, through the motor 826, through the conductor 821, through the contacts 828 Y(now closed) of the hook switch 819, through the conductor 829, through the contacts 838' (now closed) of the relay 824, through the conductors 8|3 and 8|4 back to the negative side of the '1l/2 volt battery.

Operation of the call switch 8|9 to calling position closes the contacts 83| to establish the following circuit including the current interrupting device 832 and the secondary of the buzzer modulating device 833, this circuit being as follows: from the positive side of the microphone battery, through the conductors 834, 835, through the secondary of the buzzer modulating device 833, through the conductor 836, through the contacts 831 (now closed) of the relay 824, through the conductor 838, through the contacts 839, through the conductor 848, through the conductor 84|, through the contacts 83| (now closed) of the call switch 8|9, through the circuit interrupting device 832, through the conductor 842, to one side of the microphone input whose other side is connected through a conductor`843 to the negative side of the microphone battery. It will be understood that the circuit interrupting device 832, as well as the other circuit interrupting devices 844, 845 and 846 are continuously rotated by the motor 826 when the latter is energized. In the case under discussion the circuit interrupting devices 844, 845 and 846 are being idly rotated since the corresponding call switches 828, 82| and 822 are in the off or non-calling position.

Energization of the relay 824, through the circuit above described, causes the contacts 838 to close, as stated, and the closure of these contacts establishes the following circuit through the primary of the buzzer modulating devices 833: from the positive side of the '1l/2 volt battery, through the conductor 888, through the primary of the buzzer modulating device 833, through the conductor 841, through the contacts 828 (now closed), through the conductor 829, through the contacts 838 (now closed) of the relay 824, through the conductors 8|3, 8|4, back to the negative side of the '7 1/2 Volt battery.

Energization of the relay 824 causes the relay contacts 848 to close to establish the following circuit through the relay 849: from the positive side of the '1l/2 volt battery, through the conductor 888, through the relay 849, through the conductor 858, through the contacts 848 (now closed) of the relay 824, through the conductors 8|3, 8|4,

back to the negative side of the 'Z1/2 volt battery.

Energization of the relay 849 causes its contacts 85| to close thereby establishing the following circuit through the transmitter control relay: from the positive side oi the '1l/2 volt battery, through the conductor 888, through the contacts 85|, (now closed) of the relay 849, through the conductor 852, through the transmitter control relay, through the conductor 853, back to the negative side of the 7 1/2 Volt battery. The transmitter control relay places the radio transmitting apparatus at station A in operation to transmit a carrier of frequency FI which carrier is modulated by the buzzer 833, the buzzer modulation being interrupted by the current interrupting device 832. In other words, by the operation of the call switch 8|9, corresponding to station B, the user at station A has now caused his apparatus to transmit a carrier frequency FI so modulated and coded by Virtue of the operation of the current interrupting devices 832 as tc select the desired station B.

Energizatiofn of the relay 849 also causes its contacts 854 to close and establish the following circuit through the relay 8H: from the positive side of the '1l/2 volt battery, through the conductors 888, 8|5, through the relay 8|1, through the conductor 8|8, through the conductor 855, through the contacts 854 (now closed) of the relay 849, through the conductor 8M, back to the negative side of the '7l/2 volt battery. 'Ihis places the radio receiving apparatus and the tube 8|8 in receptive condition as above described.

Energization-of the relay 824 causes its contacts 856 to close thereby energizing the relay 851 in the following circuit: from the positive side of the '1l/2 volt battery, through the conductors 888, 8|5, through the relay 851, through the conductor 858, through the contacts 856 (now closed) of the relay 824, through the conductors 8|3, 8|4, back to the negative side of the 1l/2 Volt battery. 'Ihe relay 851 when energized closes its contacts 859 to energize the circuit of a suitable motor driven wave changing device (not shown) Whereby the radio receiving apparatus at the station under consideration is automatically tuned to receive the frequency F2. When the contacts 859 open upon subsequent deenergization of the relay 851, the motor automatically restores the wave changing device so as to restore the tuning of the radio receiver to the frequency Fl.

Instead of the motor-operated wave-changing control which I have described above, other forms of wave-changing apparatus may be employed. For example, in Fig. 1 of Australian Patent No. 23,313/35, for Improvements in or relating to wave signaling systems, accepted July l, 1936, and in Fig. '1 of British Patent No. 459,235, for Improvements in or relating to radio wave signalling systems, granted April l, 1937 (each of said patents being issued to Wallace & Tiernan Products, Inc.), there is shown a comparatively simple form of wave-changing arrangement, controlled by a relay such as relay 851 of Fig. 4, and arranged so that the radio receiving apparatus is tuned to one frequency, such as F2, when the relay is energized, and is tuned to another frequency, such as FI, when the relay is deenergized.

Attention is now again directed to the system shown in Fig. 4.

Energization of the relay 824 at Station A causes the contacts 868 to open and the contacts 86| to close whereby the selective relay 862 is disconnected from the plate of the tube 8|8 and the relay 863 is connected to the plate of that 

